This invention relates to can ends, and particularly to ends for cans filled with food or non-carbonated beverages.
In cans for carbonated beverages the internal pressure generated by the carbon dioxide content of the product contributes significant strength to the very thin sidewalls of the cans. In contrast, non-carbonated products are frequently hot filled into cans and when such cans are cooled an internal vacuum is developed. This dictates that the can walls should be relatively thick to withstand the vacuum without collapsing or panelling. Much effort has been devoted to methods intended to ensure that the pressure in the headspace of the can containing a non-carbonated product is maintained at a pressure significantly above atmospheric throughout its storage life, thereby facilitating the use of lightweight DWI cans for such products. Mechanical pressurisation processes have been proposed in U.S. Pat. No. 4,836,398 and EP 0521642A. In these proposals, the can is provided with at least one deformable wall element, generally in the top or bottom end of the can, which is deformed after filling and seaming to reduce the internal volume of the can and thus to increase the internal pressure. The present invention seeks to provide a deformable can end of this type, as well as an efficient and reliable manufacturing process for such a can end.
Accordingly, a presently-preferred method of manufacturing a can end comprises forming an end shell comprising a radially outer seaming flange, a chuck wall adjacent the seaming flange, a center panel, and an axially downward countersink joining the center panel to the chuck wall below the level of the seaming flange. The method also comprises converting the shell to an easy-open can end by forming a score on a portion of the center panel, raising a rivet on the center panel, forming a tab and attaching the tab to the rivet, and subsequently forming the end by moving the center panel and the seaming flange one with respect to the other to raise the center panel above the level of the seaming flange.
Another presently-preferred method of manufacturing a can end comprises forming an end shell comprising a radially outer seaming flange, a chuck wall adjacent the seaming flange, a center panel, and an axially downward countersink joining the center panel to the chuck wall below the level of the seaming flange. The method also comprises converting the shell to an easy-open can end by forming a score on a portion of the center panel, raising a rivet on the center panel, and forming a tab and attaching the tab to the rivet. The method further comprises subsequently forming the end by moving the center panel and the seaming flange one with respect to the other to raise the center panel above the level of the seaming flange, and securing the end to a can body which has been filled with product. The method also comprises performing a second reforming operation on the can end to move the center panel and the seaming flange one with respect to the other to lower the center panel to a height below the level of the seaming flange, thereby reducing the headspace within the package.
Another presently-preferred method of manufacturing a can end comprises forming an end shell comprising a radially outer seaming flange, a chuck wall adjacent the seaming flange, a center panel, and an axially downward countersink joining the center panel to the chuck wall below the level of the seaming flange. The method also comprises supporting the end shell on a carrier belt, and moving the carrier belt to transport the end shell to a conversion station, where the shell is converted to an easy-open end by forming a score on a portion of the center panel, raising a rivet on the center panel, and forming a tab and attaching the tab to the rivet. The method further comprises moving the carrier belt to transport the converted end to a reform station, where the end is reformed by moving the center panel and the seaming flange one with respect to the other to raise the center panel above the level of the seaming flange.
Another presently-preferred method of manufacturing a can end comprises forming an end shell from an aluminum alloy material having a thickness of approximately 0.22 mm or less and a proof strength of approximately 250 N/mm2 or less so that the end shell comprises a radially outer seaming flange, a chuck wall adjacent the seaming flange, a center panel, and an axially downward countersink joining the center panel to the chuck wall below the level of the seaming flange. The method also comprises converting the shell to an easy-open can end by forming a score on a portion of the center panel, raising a rivet on the center panel, and forming a tab and attaching the tab to the rivet. The method further comprises subsequently forming the end by moving the center panel and the seaming flange one with respect to the other to raise the center panel above the level of the seaming flange.
The invention also provides an easy-open can end formed from one of a 3000 series aluminum alloy, a 5000 series aluminum alloy, and an 8000 series aluminum alloy, the end being formed from a material having a thickness of approximately 0.22 mm or less and a proof strength of approximately 225 N/mm2 or less.